1. Field of the Invention
The present invention relates to a reflux structure for blow-by gas that returns blow-by gas (uncombusted gas) in an engine to a clean side of an air cleaner to reflux the blow-by gas to the engine.
2. Description of the Related Art
In an engine of a motorcycle, the blow-by gas leaking from a gap between a piston and a cylinder is refluxed to an intake system of the engine and recombusted to prevent air pollution (see, for example, Patent Document 1). As the reflux structure, there is proposed a reflux structure in which a partition wall is provided in the air cleaner to form a breather chamber. To the breather chamber of the air cleaner, an engine case is connected via a breather hose. The blow-by gas generated in the engine flows into the breather chamber of the air cleaner via the breather hose. Then, the blow-by gas is inflated in the breather chamber to be decreased in flow velocity and then mixed with intake air flowing into the clean side, and the mixture is sent from an air funnel to a combustion chamber of the engine.    [Patent Document 1] Japanese Laid-open Patent Publication No. 59-206609
Incidentally, when the capacity of the breather chamber is decreased, the pressure loss in a path of the blow-by gas increases to increase the resistance acting on the piston, resulting in decreased engine power. On the other hand, when a sufficient capacity is ensured for the breather chamber in order to avoid the engine resistance, the intake amount from the air cleaner is reduced, resulting in decreased engine power. Since there is a trade-off relationship between the capacity of the breather chamber in the air cleaner and the engine resistance as described above, the engine power is hard to increase. Further, in a multi-cylinder engine, a large amount of blow-by gas is taken into the air funnel closest to the breather chamber because of the arrangement of the breather chamber, so that there is deviation in intake amount of the blow-by gas among cylinders.